Polycrystalline Silicon Wafer Unidirectional Solidification
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Solution Overview
Problem
The production of large-sized monocrystalline silicon wafers with diameters of 450 mm or more faces challenges in mass production, quality, and cost, particularly in achieving mechanical properties, surface cleanliness, and sagging behavior similar to monocrystalline silicon wafers, which limits their supply and usage as dummy wafers for semiconductors.
Innovation Solution
A polycrystalline silicon wafer is produced using a unidirectional solidification method with a (311) plane orientation, achieving a diameter of 450 mm or more, a thickness of 900 μm or more, and an average crystal grain size of 5 to 50 mm, with surface roughness of 1 nm or less, and impurity concentrations below 1×10^10 atoms/cm², to mimic the properties of monocrystalline silicon wafers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If monocrystalline silicon wafers with diameter of 450 mm or more are produced using conventional methods, then the wafer size is increased, but the production cost increases significantly and mass production becomes difficult
Solution Approach 1:
The patent applies this principle by using polycrystalline silicon ingots instead of expensive monocrystalline silicon ingots to produce dummy wafers. The polycrystalline material, which is cheaper and easier to manufacture, is used to create wafers that fulfill the functional requirements for dummy wafers in semiconductor production, thereby reducing production costs while maintaining the required wafer diameter of 450 mm or more
Solution Approach 2:
The patent changes the material parameter from monocrystalline silicon to polycrystalline silicon, and controls the crystal grain size parameter within the range of 1 to 10 μm through specific sintering conditions. This parameter change enables the production of large-diameter wafers at lower cost while achieving mechanical properties and surface characteristics suitable for dummy wafer applications
2Ease of manufacture
If polycrystalline silicon wafers are used as dummy wafers, then the cost is reduced, but the surface roughness and mechanical properties differ significantly from monocrystalline silicon wafers
Solution Approach 1:
The patent controls the crystal grain size parameter within the range of 1 to 10 μm through specific sintering conditions and applies surface treatment processes to achieve surface roughness Ra of 0.2 to 2 μm. These parameter changes enable polycrystalline silicon wafers to achieve surface quality and mechanical properties comparable to monocrystalline silicon wafers, making them suitable for dummy wafer applications
Solution Approach 2:
The patent applies different processing conditions to different aspects of the polycrystalline silicon material: controlling crystal grain size in the bulk material to achieve appropriate mechanical properties, and applying surface treatment to achieve the required surface roughness. This local quality approach ensures that each property is optimized independently to match monocrystalline silicon specifications
3Strength
If conventional sintered silicon wafers with small crystal grain size are used, then the mechanical strength is increased, but the wafer gravitational sag deviates from monocrystalline silicon wafers
Solution Approach 1:
The patent optimizes the crystal grain size parameter within the range of 1 to 10 μm and controls the porosity parameter within 5 to 20% through specific sintering conditions. These parameter changes achieve a balance between mechanical strength and gravitational sag characteristics, making the polycrystalline silicon wafers suitable for dummy wafer applications where both properties are important
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The resulting polycrystalline silicon wafer exhibits mechanical properties and surface characteristics similar to monocrystalline silicon wafers, enhancing its suitability as a dummy wafer and reducing manufacturing costs by improving yield and surface cleanliness.
Implementation Method 1
silicon ingots produced by unidirectional solidification after heat melting are used
Data Source
AI summary
Provided is a polycrystalline silicon wafer produced by a melting and unidirectional solidification method, where the polycrystalline silicon wafer has a diameter of 450 mm or more, a thickness of 900 μm or more, and an average crystal grain size of 5 to 50 mm, and is made up of one piece. The present invention provides a large-sized polycrystalline silicon wafer having a wafer size of 450 mm or more, of which: mechanical properties are similar to those of monocrystalline silicon wafers; the crystal size is large; the surface roughness is low; the surface has a high cleanliness; the polished surface has less unevenness by having a definite crystal orientation; and the sag value is similar to that of monocrystalline silicon wafers.